When using dies under pressure more than an allowable value in a press brake, there is the risk of breakage which is very dangerous for the operator. Therefore, press brakes of the above type are generally provided with an overload protector which restricts the pressure of the ram for driving the movable die so as not to exceed an allowable value.
One of conventional overload protectors is disclosed in Japanese Patent Publication (KOKAI) Gazette No. 6-154871 (1994) according to which the pressure applied between the upper and lower dies is detected and if it is determined from the detected value that an abnormal condition or overload condition has occurred, the press brake is brought to an emergency stop.
Although the pressure can be constantly checked in the method disclosed in this publication, it disadvantageously requires a specialized device for pressure detection. In addition, a pressure high enough to cause die breakage is exerted between the upper die (punch) and the lower die (die) until an abnormal condition is detected and the dies are, therefore, susceptible to damage. In cases where the ram which supports the movable die is driven by servo motors, the ram moves at high speed. Therefore, there is the possibility that the pressure caused by the movement of the ram cannot be detected in time so that the dies will be broken before detecting overload.
The present invention is directed to overcoming the foregoing problems, and the prime object of the invention is therefore to provide a ram control method and a ram control system adapted for use in a press brake, which are capable of avoiding the risk of die breakage due to collision caused by input errors of bending data, without use of an additional, specialized device for pressure detection.